What Are Manufacturing Defects in an IC?
Manufacturing defects are unintentional defects get introduced during the fabrication process of an IC. These defects can alter the electrical behavior of the IC, causing it to malfunction or fail entirely.
Common Types of Manufacturing Defects in ICs
1. Open Circuit (Open Faults)
Occurs when a metal line or connection is broken.
Result: No current flows → signal never reaches its destination.
Example: A gate input is floating due to an unconnected wire.
2. Short Circuit (Bridging Faults)
Two or more signal lines that should be separate are shorted together.
Result: Incorrect logic values due to interference.
3. Stuck-at Faults
A node is permanently stuck at 0 or 1, regardless of the actual logic.
Common model used for test generation (as we discussed earlier).
4. Via or Contact Failures
Issues in the via (vertical interconnect) between metal layers.
Can cause open circuits or resistance-related delays.
5. Gate Oxide Defects
Damage or contamination in the transistor's oxide layer.
Can lead to leakage currents, transistor malfunction, or breakdown.
6. Parametric Defects
Subtle variations in parameters like threshold voltage (Vt), line width, or capacitance.
These may not cause outright failures but can cause timing violations or marginal operation.
7. Latch-Up
A condition where parasitic components form a short-circuit path, causing excessive current flow.
Can permanently damage the chip if not mitigated.
How Are These Defects Detected?
- DFT (Design for Testability) techniques: scan chains, BIST.
- ATPG (Automatic Test Pattern Generation): for stuck-at and bridging faults.
- Parametric Testing: checks leakage, delay, and timing margins.
- Yield Analysis: monitors wafer-level defect trends.
- Lower yield (good chips per wafer).
- Reduced reliability and lifetime.
- Increased cost and test complexity.
- Need for burn-in and stress testing in high-reliability applications.
